Numerical dissipation switch for two-dimensional central-upwind schemes

We propose a numerical dissipation switch, which helps to control the amount of numerical dissipation present in central-upwind schemes. Our main goal is to reduce the numerical dissipation without risking oscillations. This goal is achieved with the help of a more accurate estimate of the local propagation speeds in the parts of the computational domain, which are near contact discontinuities and shears. To this end, we introduce a switch parameter, which depends on the distributions of energy in the x- and y-directions. The resulting new central-upwind is tested on a number of numerical examples, which demonstrate the superiority of the proposed method over the original central-upwind scheme.

Identifying important nodes affecting network security in complex networks

An important node identification algorithm based on an improved structural hole and K-shell decomposition algorithm is proposed to identify important nodes that affect security in complex networks. We consider the global structure of a network and propose a network security evaluation index of important nodes that is free of prior knowledge of network organization based on the degree of nodes and nearest neighborhood information. A node information control ability index is proposed according to the structural hole characteristics of nodes. An algorithm ranks the importance of nodes based on the above two indices and the nodes’ local propagation ability. The influence of nodes on network security and their own propagation ability are analyzed by experiments through the evaluation indices of network efficiency, network maximum connectivity coefficient, and Kendall coefficient. Experimental results show that the proposed algorithm can improve the accuracy of important node identification; this analysis has applications in monitoring network security.

Changes in the location of the nucleation point of slip events on ancient normal faults

<p>The lack of an unambiguous method for determining the propagation direction of slip events on faults over significant time periods limits our understanding of the long-term stability of fault slip propagation directions. A geological means for determining the propagation direction of slip events during the growth of faults is provided by mutually cross-cutting faults and bed-parallel slip-surfaces in the Ptolemais Basin, northern Greece.</p><p>In the Kardia lignite mine, Ptolemais Basin, bed-parallel slip surfaces intermittently offset the Quaternary faults as they grew to form discontinuities on otherwise continuous fault surfaces. Subsequent fault slip increments bypassed these discontinuities to re-establish a continuous fault trace and leave an associated ‘dead’ splay. The geometry and displacement distributions at these fault/bed-parallel slip intersections record the fault displacement at the time of bed-parallel slip and whether the next fault slip increment had an upwards or downwards component to its local propagation vector.</p><p>A database (N = 88) of slip propagation directions and fault throws was derived from continuous mapping of mine faces during lignite extraction over an eight year period. The data demonstrate a clear relationship between slip propagation direction and the accumulation of fault displacement on individual faults. During the early stages of fault growth, slip events propagated almost exclusively upwards through the mined sequence, but later stages of growth are marked by slip events showing both upward and downward components of propagation. The data therefore demonstrate that the location of the point of initiation of fault slip events on these Quaternary faults varied over the fault surfaces as the faults grew.</p><p>The emergence of systematic results from our analyses suggests that cross-cutting relationships between other synchronously active structures (e.g. conjugate faults) can provide a robust means for determining the propagation directions of slip events on ancient faults at outcrop.</p>

Using cellular automata to simulate wildfire propagation and to assist in fire prevention and fighting

Cellular Automata have been successfully applied to simulate the propagation of wildfires with the aim of assisting fire managers in defining fire suppression tactics and in designing fire risk management policies. We present a Cellular Automata designed to simulate a severe wildfire episode that took place in Algarve (southern Portugal) in July 2012. During the episode almost 25 thousand hectares burned and there was an explosive stage between 25 and 33 h after the onset. Results obtained show that the explosive stage is adequately modeled when introducing a non-local propagation rule where fire is allowed to spread to the nearest and next nearest cells depending on wind speed. When the rule is introduced deviations in modeled time of burning from estimated time based on hotspots detected from satellite have a root mean square difference of 8.7 hours for a simulation period of 46 h (less than 20 %). The simulated pattern of probabilities of burning as estimated from an ensemble of 100 simulations show a marked decrease out of the limits of the observed scar, indicating that the model represents an added value for fire fighting in what respects to the choice of locations to allocate resources for fire combat.